Communication System And Method For Minimum Burst Duration

ABSTRACT

A system and method for providing a minimum burst duration in accordance with a regional standard and/or requirement. One embodiment comprises a first interface ( 204 ) configured to receive data to be communicated, a memory ( 208 ) configured to store a value corresponding to a regional minimum duration, a processor ( 202 ) configured to generate a frame, configured to compare a duration of the generated frame with the regional minimum duration, configured to add at least one padding symbol to the generated frame to generate a second frame, the second frame having a duration at least equal to the regional minimum duration, and a second interface ( 206 ) configured to communicate the second frame onto a communication channel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/513,561 filed on Nov. 3, 2004, which is a national stage entry ofPCT/US03/14179 filed on May 5, 2003, which claims priority to, and thebenefit of, the filing date of Provisional Application Ser. No.60/380,036 entitled “COMMUNICATION SYSTEM AND METHOD FOR MINIMUM BURSTDURATION” filed on May 6, 2002, each of which is hereby incorporated byreference.

TECHNICAL FIELD

The present invention relates generally to communications systems, andmore particularly, to a system and method for a digital communicationdata formats.

BACKGROUND

Data communication occurs as the transfer of information from onecommunication device to another. In some devices, data communicationsare accomplished by the use of a modem located at each communicationendpoint. In the past, the term “modem” denoted a piece of communicationapparatus that performed a modulation and demodulation function, hencethe term modem. Today, the term modem is typically used to denote anypiece of communication apparatus that enables the transfer of data andvoice information from one location to another. For example, modemcommunication systems use many different technologies to perform thetransfer of information from one location to another.

Digital subscriber line (DSL) technology is one vehicle for suchtransfer of information. DSL technology uses the widely availablesubscriber loop, the copper wire pair that extends from a telephonecompany central office to a residential location, over whichcommunication services, including the exchange of voice and data, may beprovisioned. DSL devices can be referred to as modems, or, moreaccurately, transceivers, which connect the telephone company centraloffice to the user, or remote location typically, referred to as thecustomer premises. DSL communication devices utilize different types ofmodulation schemes and achieve widely varying communication rates.However, even the slowest DSL communications devices achieve data ratesfar in excess of conventional point-to-point modems.

DSL transceivers can be used to provision a variety of communicationservices using, for example, but not limited to, asynchronous transfermode (ATM). ATM defines a communication protocol in which data cells areused to carry information over the DSL communication channel. The firstportion of the ATM cell is typically used for overhead and the remainingportion is used to carry the communicated information or data. Whenusing a switched-carrier transmission methodology, a control transceivermay be connected via the DSL to one or more remote transceivers. In sucha communication scheme, the transmission is commonly referred to as“half-duplex,” which is defined as two way electronic communication thattakes place in only one direction at a time. With only a single remotetransceiver on a line, switched-carrier transmission may instead beemployed in full-duplex mode (allowing transmission in both directionssimultaneously). In this case, full-duplex operation is typicallyenabled by employing either echo cancellation or frequency divisionmultiplexing. Hybrid techniques are possible such as one in which thereare multiple remote transceivers and communication takes place betweenthe control transceiver and only one remote transceiver in full-duplexfashion.

Before the transmission of ATM cells, a preamble containing channel,transmission, address and administrative information may be transmittedby the transceiver. The application of this preamble is sometimesreferred to as “framing” the data to be transmitted. The resultingsequence of symbols assembled. for transmission, including preamble and(possibly) cells, is then referred to as a “frame”. Due to theswitched-carrier nature of the transmission, silence precedes thispreamble. It is desirable to have the ability to precisely delimit thebeginning and end of a transmission to within one transmitted symbolinterval. Robustly delimiting the beginning of a frame enables areceiving transceiver to reliably begin decoding the frame at thecorrect symbol. Likewise, robustly delimiting at the end of a frameenables a receiving transceiver to reliably decode the entire framethrough the final symbol, and then stopping so as to prevent data lossand to prevent the inclusion of any false data. Furthermore, bycommunicating an end of frame indicator to a receiving transceiver priorto the actual end of the frame, line turnaround time (i.e., idle time onthe line between transmissions) can be reduced, thereby increasing theeffective use of the available line bandwidth.

Because the most efficient signal constellation encoding cannot allocatesignal space to silence, it is impractical to reliably discriminatesilence from a signal when analyzing only a single symbol encoding anarbitrary data value. To improve frame delimiting, existing techniquesuse special marker symbols whose symbol indices are greater than thoseused to encode data. At N bits per symbol (bps), data is encoded usingsymbol indices 0 through 2^(N)−1. The special symbols use indices 2^(N)and above. While these special marker symbols are useful for marking thebeginning and end of a transmission, their placement at the outer edgesof a constellation raises the peak signal, thus increasing the peak toaverage ratio (PAR) across all data rates by as much as 4 dB.Unfortunately, discrimination of special symbols has the same errorthreshold as does decoding of data.

DSL systems typically operate in the presence of crosstalk from otherDSL systems in the same loop plant (a communication system having aplurality of subscriber loops, where portions of the subscriber loopsshare a common location and are in close proximity to each other).Crosstalk is generated when a signal transmitted on one pair of wirescouples electromagnetically to a nearby pair of wires to create anunwanted signal which is received together with the intended signal. DSLsystems use a variety of techniques to adapt to crosstalk, as well asthe distortion introduced by the loop and other impairments. In orderfor a receiver residing in the transceiver to adapt to crosstalk, thecrosstalk must be detectable.

DSL systems which use burst transmission are generally known asShort-Term Stationary (STS) systems. DSL systems are characterized bytwo distinct transmission states. An STS transceiver alternates betweenan ON state, in which a signal is transmitted, and an OFF state, inwhich either silence or a lower power and/or lower bandwidth signal istransmitted. The duration of individual ON and OFF periods may varybased on the presence of data to transmit and other factors. If the ONduration of a signal is significantly shorter than the minimum timeperiod in which another DSL system can detect noise, the crosstalk maynot be detected correctly. As a result, American National StandardsInstitute (ANSI) standard T1.417-2001 (Spectrum Management for LoopTransmission Systems), incorporated by reference herein, includes arequirement that the minimum transmission time for any transmissionburst be at least 246 microseconds. See T1.417-2001 for additionalbackground information on crosstalk, short-term stationary systems, andspectral compatibility requirements. It is possible that other regionalrequirements could be written that specify a different minimumtransmission time.

One DSL method and apparatui meets the T1.417 requirement by adding afixed number of padding symbols to empty frames to extend the length ofthose frames to the required, predefined minimum time. Such a DSL systemis configured to operate in the United States and other regionalcommunication systems that employ the T1.417 requirement.

In asynchronous transfer mode (ATM) cell based systems, transmissionscan be extended in increments of one cell transmission period. However,this may be excessive relative to customer-specific requirements. Theend-of-pad indication of the present invention allows a resolution toone symbol period even under poor communication conditions. Key systemrequirements such as scrambler initialization require accurate detectionof the last symbol in the message. In modulation a false detection ofthe:last symbol will cause a faulty upstream scrambler initializationand undetectable upstream data.

Other DSL systems are configtired to operate in the other regionalcommunication systems that employ standards and/or requirements that aredifferent from the T1.417 requirement. Accordingly, equipment configuredto operate under the T1.417 requirement may not be suitable foroperation under other standards and/or requirements. When DSL equipmentis to operate in regions having different standards and/or requirements,the equipment must be configured to operate using the standards and/orrequirements of the region in which it is installed.

Having a variety of different DSL devices configured to operate under avariety of standards and/or requirements is undesirable because of theadded cost to develop, manufacture and maintain separate DSL devices ina variety of locations, each location having different standards and/orrequirements. Furthermore, the DSL equipment, once manufactured for aparticular standard and/or requirement, is not interchangeable with DSLequipment used in another region having a different standard orrequirement. Accordingly, if a DSL device, or one of its components,fails in the field, the failed device or component must be replacedusing a device or component configured for operation under thatparticular standard and/or requirement. That is, a readily available“off-the-shelf” device or component cannot be used.

SUMMARY

The present invention provides an system and method for providing aminimum burst duration in accordance with a regional standard and/orrequirement. The minimum duration can be changed locally or remotely, toconfigure each device after deployment, without requiringsynchronization of the change in the devices at each end of acommunications channel. One embodiment comprises a first interfaceconfigured to receive data to be communicated, a memory configured tostore a value corresponding to a regional minimum duration, a processorconfigured to generate a frame, configured to compare a duration of thegenerated frame with the regional minimum duration, configured to add atleast one padding symbol to the generated frame to generate a secondframe, the second frame having a duration at least equal to the regionalminimum duration, and a second interface configured to communicate thesecond frame onto a communication channel.

Another embodiment is characterized as a process comprising generating aframe for transmission, comparing a duration of the generated frame witha minimum duration, adding at least one padding symbol to the generatedframe such that a duration of a second frame is increased at least to apredetermined duration corresponding to at least the minimum duration,and communicating the second frame.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood with reference to the followingdrawings. The components in the drawings are not necessarily to scale,emphasis instead being placed upon clearly illustrating the principlesof the present invention. Moreover, in the drawings, like referencenumerals designate corresponding parts throughout the several views.

FIG. 1 is a schematic view illustrating a communication environment inwhich embodiments of DSL transceivers configured according to thepresent invention reside.

FIG. 2 is a block diagram illustrating an embodiment of a variable burstduration system implemented in the CO DSL transceiver and the CP DSLtransceivers of FIG. 1.

FIG. 3A is a schematic view illustrating the bit to symbol relationshipof a data frame communication having data.

FIG. 3B is a schematic view illustrating the bit to symbol relationshipof a data frame communication having no data with padding in accordancewith embodiments of the present invention.

FIG. 4 is a block diagram illustrating another embodiment of a variableburst duration system implemented in the CO DSL transceiver and the CPDSL transceivers of FIG. 1.

FIG. 5 is a flow chart illustrating one embodiment of the operation ofthe variable padding logic.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Although, described with particular reference to the transmission ofasynchronous transfer mode (ATM) cells or the like over a digitalsubscriber loop (DSL) communication channel, the system and method for avariable burst duration system 200, which provides for a variableminimum burst duration, can be implemented to transmit all forms of datain any switched-carrier transmission system in which it is desirable toadjust the burst duration (corresponding to the frame length) of agenerated frame to ensure that minimum burst duration of thecommunicated frame satisfies a particular standard and/or requirement.

The specified minimum burst duration for a communicated framecorresponds to the size of the frame. In some situations, such as aheader-only frame, the generated header-only frame burst duration(corresponding to the frame length) is less that the specified minimumburst duration. Accordingly, embodiments of the variable burst durationsystem 200 extend the burst duration (or frame length) of such aheader-only frame, or other types of frames which have a duration lessthan the specified minimum burst duration. One embodiment adds orinserts padding symbols onto the frame to extend the burst duration toat least satisfy the specified minimum burst duration. Sudh a process isreferred to herein as “header padding” for convenience. The paddingsymbol may be any suitable symbol, such as one comprising binary “zeros”or the like.

FIG. 1 is a schematic view illustrating a communication environment 100,such as, but not limited to, a switched-carrier half-duplex system, inwhich embodiments of DSL transceivers configured according to thepresent invention reside, referred to herein as a variable burstduration system 200 (FIG. 2). The exemplary communication environment100, includes central office 102 connected via communication channel 104to customer premises 106. Communication channel 104 can be any physicalmedium over which communications signals can be exchanged. In oneembodiment, communication channel 104 is the copper wire pair thatextends from a telephone company central office to an end-user location,such as a home or office, referred to herein for convenience as thecustomer premises 106. Furthermore, communication channel 104 mayterminate in any suitable location having communication equipmentdescribed herein and configured in accordance with—the presentinvention.

Central office 102 includes a central office (CO) DSL transceiver 108connected to communication channel 104. For convenience, the term“transceiver” includes a plurality of components configured to bothtransmit and receive communications. An illustrative example of atransceiver is a modem. It is understood that any suitable transceiverdevice may be configured with embodiments of the present invention.

CO DSL transceiver 108 processes data received from an external system110, received via connection 112. Non-limiting examples of an externalsystem include a public switched telephony system, a frame relay systemor the Internet. It is understood that embodiments of the presentinvention are not, limited by the nature of the external system 110which communicates with CO DSL transceiver 108. Furthermore, eitheranalog or digital communications may be communicated between theexternal system 110 and the DSL transceiver 108.

Customer premises 106 includes one or more customer premises (CP) DSLtransceivers 112. DSL transceivers are connected, via the CP wiring 114residing in the customer premises 106, to communication channel 104. TheCP wiring 114 can be, for example but not limited to, the telephonewiring network within a private residence or within an office (thecustomer premises 106). Other suitable communication mediums may also beemployed. CP DSL transceivers 112 can be connected to a variety of dataterminal equipment (DTE) devices located at customer premises 106.

Although a variable burst duration system 200 will be described below ina half-duplex communication environment for convenience, the CO DSLtransceiver 108 and the CP DSL transceiver 1-12 implemented withembodiments of the present invention may be used in a switched-carrierfull-duplex environment as well. In such a case, full-duplex operationmay be enabled using technologies such as echo cancellation or frequencydivision multiplexing.

Examples of embodiments of the present invention implemented in or withDTE devices include, but are not limited to, computer terminal 116.Other types of DTE device embodiments may include digital telephonedevices, Internet television devices, audio and multimedia devices,facsimile (fax) devices, graphic devices, high-speed Internet devices,high-speed local access network (LAN) devices, Internet telephonedevices, stereo/audio devices, digital television devices, digital.video cassette recorder devices, utility meter devices, home Managementand security devices. Operation of such DTE devices are generallyunderstood and are not further described since the embodiments of thepresent invention are easily configured to operate in or with theparticular DTE device in which it is implemented.

Accordingly, CO DSL transceiver 108 communicates digital data, viacommunication channel 104, to the CP DSL transceiver 112, which thencommunicates the data to the above-described DTE device, to which it isconnected to. For example, CP DSL transceiver 112, also referred to as amodern, is illustrated for convenience as connecting to computerterminal 116, via connection 118. CP DSL transceiver 112 may be anexternal component or reside within the computer terminal 116. Thus,computer terminal 116 may communicate data to a remote device (notshown) by communicating the data in a first format to the CP DSLtransceiver 112. CP DSL transceiver converts the received data into asecond format, in accordance with the present invention, andcommunicates the data in the second format to the CO DSL transceiver108, via communication channel 104. The DSL transceiver thencommunicates the data onto the external system 110 in a suitable format.Communication of data from the remote device directed to the computerterminal 116 are communicated over the above-described path in a reversedirection.

Furthermore, additional DSL transceivers 120 can be located at customerpremises 106. Accordingly, multipoint DSL operation between a pluralityof customer premises DTE devices, such as computer terminal 122, and theCO DSL transceiver 108 may be supported by embodiments of the presentinvention. Frequency multiplexing and/or time domain multiplexing may beemployed. The aspects of the invention discussed herein are applicableto both one CP. DSL transceiver 112, or to a plurality of CP DSLtransceiver 120, located at customer premises 106.

In addition, analog type devices residing at the customer premises 106may simultaneously communicate over the communication channel 104 withanother device (not shown) residing in the central office 102. Anexample of an analog type customer premises device is an analogtelephone 124. Such analog devices communicate using a different channel(frequency spectrum) than the channels used by the DTE devicesconfigured to communicate in accordance with the present invention. Forexample, an analog telephone communicates using the zero to 4 kHzfrequency band, while DTE devices communicate at frequencies greaterthan 4 kHz. Operation of such analog communication devices are generallyunderstood and are not further described herein.

FIG. 2 is a block diagram illustrating an embodiment of a variable burstduration system 200 implemented in the CO DSL transceiver 102 and the CPDSL transceivers 112, 120 (FIG. 1). The variable burst duration system200 includes a processor 202, a first interface 204, a second interface206 and a memory 208. Processor 202, first interface 204, secondinterface 206 and memory 208 are communicatively coupled throughcommunications bus 210, via connections 212, 214, 216 and 218respectively, thereby providing connectivity between the above-describedcomponents. In alternative embodiments of a variable burst durationsystem 200, the above-described components are connectively coupled in adifferent manner than illustrated in FIG. 2. For example, one or more ofthe above-described components may be directly coupled to each other ormay be coupled to each other via intermediary components (not shown).Furthermore, embodiments of the present invention may be implemented inany suitable transceiver configured to communicate using frames.

One embodiment of memory 208 further includes the information formattingand communication logic 220, the variable padding logic 222 and theregional minimum burst duration 224. The variable burst duration system200, described in greater detail below, resides as firmware, software orother computer-readable medium executed by processor 202. Forconvenience, the information formatting and communication logic 220, andthe variable padding logic 222, are illustrated as separate logicalunits. In another embodiment, the information formatting andcommunication logic 220, and the variable padding logic 222, areintegrated together into a single logical unit.

In an embodiment of the variable burst duration system 200 implementedin the CO DSL transceiver 108 (FIG. 1), the above describedcommunication channel 104 is coupled to the variable burst durationsystem 200 at the second interface 206. Thus, a communication from a CPDSL transceiver 112, 120 (FIG. 1) is received by the second interface206, and is processed into a format that is communicated to theprocessor 202. Processor 202, while executing the information formattingand communication logic 220, can then process the receivedcommunication. The received communication is then further processed andtransmitted onto connection 112, via the first interface 204.Accordingly, communications are processed into a suitable format fortransmission to the external system 110 (FIG. 1) by processor 202, whileexecuting the information formatting and communication logic 220.Similarly, communications from the external system 110 are received bythe variable burst duration system 200 via the first interface 204, thecommunication is processed by processor 202 while executing theinformation formatting and communication logic 220, and then transmittedto a destination CP DSL transceiver 112, 120, via the second interface206. Detailed processes of receiving and transmitting communications bya CO DSL transceiver 108, and the associated formatting of thosecommunications, are not described in greater detail other than to theextent necessary. to describe the operation of embodiments of thepresent invention.

In an embodiment of the variable burst duration system 200 implementedin one of the CP DSL transceivers 112, 120 (FIG. 1), the above describedcommunication channel 104 is coupled to the variable burst durationsystem 200 at the second interface 206. Thus, a communication from a CPDSL transceiver 112, 120 (FIG. 1) is received by the second interface206, and is processed into a format that is communicated to theprocessor 202. Processor 202, while executing the information formattingand communication logic 220, can then process the receivedcommunication. The received communication is then further processed andtransmitted to a CP DTE device, such as computer terminal 118 (FIG. 1),via the first interface 204. Accordingly, communications are processedinto a suitable format for transmission to the computer terminal 118 byprocessor 202, while executing the information formatting andcommunication logic 220. Similarly, communications from the computerterminal 118 are received by the variable burst duration system 200 viathe first interface 204, the communication is processed by processor 202while executing the information formatting and communication logic 220,and then transmitted to the CO DSL transceiver 108 via the secondinterface 206. Detailed processes of receiving and transmittingcommunications by a CP DSL transceiver 112, 120, and the associatedformatting of those communications, are not described in greater detailherein other than to the extent necessary to describe the operation ofembodiments of the present invention.

FIG. 3A is a schematic view illustrating the bit to symbol relationshipof an exemplary data frame communication having data. FIG. 3B is aschematic view illustrating the bit to symbol relationship of anexemplary data frame communication having no data with padding symbolsadded to the frame in accordance with embodiments of the presentinvention such that minimum burst duration requirements are satisfied.

As described above, DSL systems which use burst transmission aregenerally known as Short-Term Stationary (STS) systems. An exemplaryasynchronous transfer mode (ATM) frame with ATM cells having data,communicated on such a system, is illustrated in FIG. 3A. Such an STSsystem may be characterized by two distinct transmission states. An STStransceiver alternates between an ON state, in which a signal istransmitted, and an OFF state, in which either silence or a lower powerand/or lower bandwidth signal is transmitted. The burst duration ofindividual ON periods may vary based on the presence of data to transmitand other factors. If the ON burst duration of a signal is significantlyshorter than the minimum burst duration in which another DSL system candetect noise, the crosstalk may not be detected correctly. To preventthis occurrence, ANSI standard T1.417 requires that any bursttransmission be at least 246 microseconds long. As noted above, it ispossible that other regional requirements could be written that specifya different minimum burst duration.

Accordingly, embodiments of the present invention provide for a singleDSL transceiver, located at either the central office 102 and/or thecustomer premises 106 (FIG. 1), to provide communications that satisfythe minimum burst duration requirements, or minimum frame lengthrequirements, of the communication environment 100 in which the DSLtransceiver is operating. Furthermore, because the regional minimumburst duration 224 (FIG. 2) described in greater detail below, and/orthe regional padding symbol value 402 (FIG. 4), may be specified, a DSLtransceiver configured with the variable burst duration system 200 ofthe present invention may be relocated to a another communicationenvironment 100 having a different minimum burst duration requirement.

One embodiment meets the T1.417 requirement, or any other minimum burstduration requirement of the particular communication environment 100 inwhich the DSL transceiver is operating in, by adding a fixed number ofpadding symbols to empty frames to extend the duration (or frame length)of those frames to the required, predefined minimum time. In theembodiment described above, the duration of an empty frame is comparedagainst the specified minimum burst duration, a difference in burstduration (or frame length) is determined, the number of padding symbolsto be added to the frame to meet the minimum burst duration isdetermined, and the padding symbols are added into the frame. In anotherembodiment, described in greater detail below, a specified number ofpadding symbols are added in to the generated frame to meet the minimumburst duration requirement. In another embodiment, frames having cells,but which have a duration less than the specified minimum burstduration, have padding symbols added into the frame in accordance withthe present invention.

Accordingly, when the CO DSL transceiver 102 (FIG. 1) generates a framethat is less than the specified regional burst duration, such as aheader-only frame, the variable padding logic 222 (FIG. 2) is executedto add padding symbols such that the communicated frame is at least theminimum burst duration required by the T1.417 requirement or theapplicable regional standard. Similarly when the CP DSL transceiver 112,120 (FIG. 1) generates a frame that is less than the specified regionalburst duration, the variable padding logic 222 is executed to addpadding symbols such that the communicated frame is at least the minimumburst duration required by the T1.417 requirement or the applicableregional standard in which the DSL transceiver is operating.

In asynchronous transfer mode (ATM) cell based systems, transmissionscan be extended in increments of a one cell transmission period.However, this may be excessive relative to customer-specificrequirements. The end-of-pad indication of the present invention,described in greater detail below, allows a resolution to one symbolperiod. Key system requirements such as scrambler initialization requireaccurate detection of the last symbol in the communicated frame. Inmodulation, a false detection of the last symbol will cause a faultyupstream scrambler initialization and undetectable upstream data.

As described herein, embodiments provide that the minimum burst duration(or frame length) is made configurable to allow for a specific regionalrequirement. The minimum burst duration requirement of the particularcommunication environment 100 in which the DSL transceiver is operatingin is specified into the regional minimum burst duration 224 region ofmemory 208 (FIG. 2). When a generated frame that is less than thespecified regional burst duration, such as a header-only frame, is to becommunicated over the communication channel 104, either by the CO DSLtransceiver 102 or the CP DSL transceiver 106 (FIG. 1), the duration (orlength) of the frame is evaluated by the variable padding logic 222(FIG. 2). The determined duration of the generated frame is comparedwith the minimum burst duration requirement of the particularcommunication environment 100 in which the DSL transceiver is operatingin, as specified in the regional minimum burst duration 224. Adifference between the generated burst duration and the minimum burstduration is determined. The determined difference causes the variablepadding logic 222 to add padding symbols into the generated frame,referred to herein as the “second generated frame” for convenience, sothat the modified frame of sufficient size to meet the minimum burstduration requirement is communicated.

FIG. 4 is a block diagram illustrating another embodiment of a variableburst duration system 200 implemented in the CO DSL transceiver 102 andthe CP DSL transceivers 112, 120 (FIG. 1). Elements common to theabove-described embodiment illustrated in FIG. 2 are not described orillustrated again for convenience. This embodiment includes in memory208 the information formatting and communication logic 220, the variablepadding logic 222 and the regional padding symbol value 402.

With this embodiment, the value, or number of, padding symbols added toan empty frame is specified in a suitable manner. Before a generatedframe having a duration that is less than the specified regional burstduration is communicated, the variable padding logic 222 is executedsuch that the specified number of padding symbols are inserted into thegenerated frame. The specified value may be the exact number of paddingsymbols to be added to meet the minimum burst duration requirements, ora greater number of padding symbols may be added to provide margin inthe length of the communicated cell.

The required minimum burst duration 224 (FIG. 2) and/or the regionalpadding symbol value 402 (FIG. 4) can be configured locally or remotelyfrom a central site or a network management system. Accordingly, thevariable padding logic 222 is configured to receive. inputs from anexternal device such that the minimum burst duration requirement of theparticular communication environment 100 in which the DSL transceiver isoperating in is specified into the regional minimum burst duration 224and/or the regional. padding symbol value 402. It is understood that anysuitable means for specifying the regional minimum burst duration 224and/or the regional padding symbol value 402 may be implemented byembodiments of the present invention. Remote configuration of theheader-only frame size is enabled by a configuration field in theEmbedded Operations Channel (EOC) register set.

The mechanism for padding the frame is improved to provide a reliableend-of-pad indication, so that reconfiguration of the minimum burstduration does not require tight synchronization between transmitting andreceiving modems. The end-of-pad indication is a low autocorrelationsequence of symbols which allows detection of the sequence in time evenin the presence of one or more symbol errors. An exemplary frame withpadding, according to the present invention, is illustrated in FIG. 3B.Other embodiments of a frame, or other burst communication formats, areconstructed in accordance with the present invention.

In one embodiment, binary zeros are encoded and scrambled to encode thetransmitted pad. Scrambling allows the receiver to perform adaptivetracking of timing and equalization parameters. One embodiment encodeseight final pad symbols with a specific data sequence which has goodautocorrelation properties signals the end of the pad. Other embodimentsuse other numbers of final pad symbols. The final pad symbols allowaccurate identification of the last symbol even in the presence of dataerrors.

Making the minimum burst duration configurable allows new regional orcustomer-specific requirements to be accommodated without requiring achange in the design and/or manufacture of the product or technology.Making remote configuration possible from a central site or networkmanagement system, in one embodiment, allows the minimum burst durationto be optimized for specific deployments without requiring differentmodels for different regions.

The addition of an end-of-pad indication allows the receiver to reliablydetect the end of a minimum length frame without knowing in advance whatthe duration of the frame is. Reliable end-of-frame detectionfacilitates a reduction, or even minimization, of turnaround time andlatency, and facilitates, or even maximizes, throughput in time duplextransmission systems.

In one embodiment, header padding is applied to header-only frames,which are transmitted when there are no ATM cells (user data, EOC, oridle) to send. The-header padding adds symbols after the end of theframe header to pad the length (increase the duration) of thetransmitted frame to the minimum time required to meet spectralcompatibility requirements.

One embodiment uses a variable size pad with delineation to meet therequired minimum transmission time in ANSI T1.417-2001. The frame sizeis made configurable in the embodinients to anticipate possiblerequirements in other regional standards that might not match the ANSIrequirement.

It is important for time duplex modulation systems to have awell-defined indication of when a frame ends. Frames which carry cellscan only end on a cell boundary and also transmit a last-frame-in-cellindicator to help with end of frame detection. Header-only frames, towhich padding applies, can be almost any integer number of symbols inlength once the padding is made configurable, so a reliable means isrequired to allow the receiver to know when the frame is ending. Oneembodiment of the variable pad incorporates a well defined sequence ofsymbols with low autocorrelation values (Barker sequence) as the last 7symbols transmitted to identify the end of the frame. Other embodimentsemploy different numbers and or types of last symbols for delineation,such as, but not limited to, an end of file (EOF) flag, a predefinedseries of ones and/or zeros, or an High-level Data Link Control (HDLC)type flag.

Accordingly, various embodiments of the present invention may providefor one or more of the following:

Configurable symbol padding to allow minimum transmission time to beoptimised to regional requirements.

Remote configuration via EOC register field.

Delineation of end-of-pad.

Barker sequence used for delineation

Padding symbols, in one embodiment, are transmitted after the headerwhen the frame does not contain any cells. Such a frame may be referredto herein as a header-only frame. The number of padding symbols requiredfor a header-only frame will vary based on the symbol rate and may alsovary based on which transceiver is transmitting, and may be reconfiguredvia the EOC. The minimum transmission time, or burst duration, for aframe is set in the regional minimum burst duration 224 and/or theregional padding symbol value 402, referred to herein as the Time DomainRestrictions Register. for convenience. The transceiver configuredaccording to the present invention uses this value to determine therequired number of padding symbols at a given symbol rate. In oneembodiment, at least 7 padding symbols are always transmitted in aheader-only frame.

In one embodiment, padding symbols are transmitted at 2 bits per symbol(bpS) and are generated from padding bits which are grouped, scrambledand encoded as specified for cell data bits. Other embodiments employpadding symbols transmitted at other rates.

The padding bits are defined as follows:

For a number of padding symbols (PS), a sequence of padding bits PB₀through PB_(2PS-1) are generated such that:

-   -   PB₀ through PB_(2PS-15)=0    -   PB_(2PS-14) through PB_(2PS-1) are defined in Table 1

In one embodiment, if PS=7 (the minimum number of padding symbols), then

PB_(2PS-14)=PB_(O) and the entire padding bits sequence consists of theend-of-padding delineation sequence defined in Table 1. The last 7padding symbols are generated from the end-of-padding delineationsequence defined in Table 1 to provide an end-of-frame indication to thereceiving CO DSL transceiver 108 or CP DSL transceiver 112, 120.

TABLE 1 End-of-padding delineation sequence j 14 13 12 11 10 9 8 7 6 5 43 2 1 PB_(2PS-j) 1 1 1 1 1 1 0 0 0 0 1 1 0 0

FIG. 5 is a flow chart 500 illustrating one embodiment of the operationof the variable padding logic 222 (FIG. 2). The flow chart 500 shows thearchitecture, functionality, and operation of a possible implementationof the software for implementing the variable burst duration system 200.In this regard, each block may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat in some alternative implementations, the functions noted in theblocks may occur out of the order noted in FIG. 5 or may includeadditional functions without departing significantly from thefunctionality of the variable burst duration system 200. For example,two blocks shown in succession in FIG. 5 may in fact be executedsubstantially concurrently, the blocks may sometimes be executed in thereverse order, or some of the blocks may not be executed in allinstances, depending upon the functionality involved, as will be furtherclarified hereinbelow. All such modifications and variations areintended to be included herein within the scope of this disclosure forthe variable burst duration system 200 and to be protected by theaccompanying claims.

The process starts at block 502, wherein the variable padding logic 222(FIG. 2) is executed by processor 202. At block 504, a regional minimumburst duration is specified. The specified regional minimum burstduration is saved in to memory 208 as described above. In anotherembodiment, a regional padding symbol value is specified. Thespecification may be made at the time of manufacture and/or distributionbased upon the intended destination of the embodiment. That is, thespecification of the regional minimum burst duration (or regionalpadding symbol value) is based upon the standards and/or requirement ofthe region to which the device is destined. Alternatively, if theembodiment is relocated or becomes subject to a different standardand/or requirement, a new regional minimum burst duration (or regionalpadding symbol value) may be specified at block 504.

At block 506 a frame is generated, including any ATM cells which havebeen received for transmission. The ATM cells may be received from a DTEdevice 118, 122 when the embodiment is at the customer premises 106, orfrom an external system 110 when the embodiments is at the centraloffice 102 (FIG. 1). There may be no ATM cells received at the time theframe is generated, in which case an empty frame is generated.

At block 508 the burst duration of the generated frame is compared withthe specified regional minimum burst duration. That is, a difference inburst duration is determined. In another embodiment, a difference inframe length is determined between the generated frame and a requiredregional minimum frame length. At block 510 a determination is madewhether the burst duration of the generated frame is at least equal tothe regional minimum burst duration. If so (the YES condition), thegenerated frame is communicated at block 512. For example, the generatedframe likely contains data such that the burst duration (or framelength) results in a burst duration that is at least equal to theregional minimum burst duration. The process then ends at block 514.

If at block 510 the burst duration of the generated frame is less thanthe regional minimum burst duration (the NO condition), the processproceeds to block 516 wherein a padding symbol is added to the generatedframe, thereby generating a second frame. The process returns to block508 and continues as described above. In one embodiment, only onepadding symbol is added to the frame. In another embodiment, apredetermined number of padding symbol are added. In yet anotherembodiment, the number of padding symbol specified in the regionalpadding symbol value 402 region of memory 208 (FIG. 4) are added to theframe. Eventually, the burst duration of the second frame is at leastequal to the regional minimum burst duration such that the second frameis communicated at block 512.

As described herein, embodiment of the system and method for a variableburst duration system 200 can be implemented in software, hardware, or acombination thereof. In a preferred embodiment(s), selected portions ofthe system and method for a variable burst duration system 200 areimplemented in hardware and software. The hardware portion of theinvention can be implemented using specialized hardware logic. Thesoftware portion can be stored in a memory and be executed by a suitableinstruction execution system (microprocessor). The hardwareimplementation of the system and method for a variable burst durationsystem 200 can include any or a combination of the followingtechnologies, which are all well known in the art: a discrete logiccircuit(s) having logic gates for implementing logic functions upon datasignals, an application specific integrated circuit havingappropriatelogic gates, a programmable gate array(s) (PGA), a field programmablegate array (FPGA), etc

Furthermore, the variable burst duration system 200 software, whichcomprises an ordered listing of executable instructions for implementinglogical functions, can be embodied in any computer-readable medium.Moreover, use by or in connection with an instruction execution system,apparatus, or device, such as a computer-based system,processor-containing system, or other system that can fetch theinstructions from the instruction execution system, apparatus, or deviceand execute the instructions.

In the context of this document, a “computer-readable medium” can be anymeans that can contain, store, communicate, propagate, or transport theprogram for use by or in connection with the instruction executionsystem, apparatus, or device. The computer readable medium can be, forexample but not limited to, an electronic, magnetic, optical,electromagnetic, infrared, or semiconductor system, apparatus, device,or propagation medium. More specific examples (a non-exhaustive list) ofthe computer-readable medium would include the following: a electricalconnection (electronic) having one or more wires, a portable computerdiskette (magnetic), a random access memory (RAM), a read-only memory(ROM), an erasable programmable read-only memory (EPROM or Flash memory)(magnetic), an optical fiber (optical), and a portable compact discread-only memory (CDROM) (optical). Note that the computer-readablemedium could even be paper or another suitable medium upon which theprogram is printed. As the program can be electronically captured, viafor instance optical scanning of the paper or other medium, thencompiled, interpreted or otherwise processed in a suitable manner ifnecessary, and then stored in a computer memory.

1. A method for extending the duration of a communicated frame, themethod comprising: generating a frame; comparing a duration of thegenerated frame with a specified minimum duration; adding at least onepadding symbol to the generated frame such that a duration of a secondframe is increased at least to a predetermined duration corresponding toat least the specified minimum duration; and communicating the secondframe.
 2. The method of claim 1, further comprising adding a lastsequence of symbols, the sequence indicating an end of the second frame.3. The method of claim 1, wherein adding the padding symbols furthercomprises varying the number of symbols added to the generated frame. 4.The method of claim 1, further comprising determining a durationdifference between the duration of the generated frame and the minimumduration.
 5. The method of claim 4, further comprising determining thenumber of padding symbols, wherein the determined number of paddingsymbols corresponds to the determined duration difference.
 6. The methodof claim 1, further comprising specifying the minimum duration.
 7. Themethod of claim 6, further comprising changing the specified minimumduration to a second minimum duration, wherein the number of paddingsymbols corresponds to the second minimum duration.
 8. A system whichextends the duration of a frame to be communicated, comprising: a firstinterface configured to receive data to be communicated; a memoryconfigured to store a value corresponding to a specified minimumduration; a processor configured to generate a frame to be communicated,configured to compare a duration of the generated frame with the minimumduration, configured to add at least one padding symbol to the generatedframe to generate a second frame, the second frame having a duration atleast equal to the minimum duration; and a second interface configuredto communicate the second frame onto a communication. channel.
 9. Thesystem of claim 8, wherein the memory further comprises a specifiedminimum duration corresponding to the specified minimum duration. 10.The system of claim 8, wherein the memory further comprises a regionalpadding symbol value corresponding to the specified regional minimumduration.
 11. The system of claim 8, wherein the System comprises atleast one selected from a group consisting of a computer terminal 116, adigital telephone device, an Internet television device, an audiodevice, a multimedia device, a facsimile (fax) device, a graphic device,a high-speed Internet device, a high-speed local access network (LAN)device, an Internet telephone device, a stereo/audio device, a digitaltelevision device, a digital video cassette recorder device, a utilitymeter device, a home management device and a security device.
 12. Asystem which extends the duration of a frame to be communicated,comprising: means for receiving data to be communicated; means forgenerating a frame; means for comparing a burst duration of thegenerated frame with a specified minimum burst duration; means foradding at least one padding symbol to the generated frame such that aburst duration of a second frame is increased at least to apredetermined burst duration corresponding to at least the specifiedminimum burst duration; and means for communicating the second frame.13. A computer-readable medium having a program for extending theduration of a communicated frame, the program comprising logicconfigured to perform the steps of: receiving a data to be communicated;generating a frame; comparing a duration of the generated frame with aspecified minimum duration; adding at least one padding symbol to thegenerated frame such that a duration of a second frame is increased atleast to a predetermined duration corresponding to at least thespecified minimum duration; and communicating the second frame.